Lindner said millions and millions of gallons of "uncontrolled water" will begin to spill over by daylight.

He said this does not mean that downtown Houston will necessarily be greatly impacted, but they don't fully know because they've never faced this situation before.

Officials released water from the Addicks and Barker reservoirs on Monday in an effort to prevent uncontrolled releases at the spillways, but that effort will not prevent the Addicks' pool level from reaching the spillover threshold of 108 feet.

"It is over 107 now," Jenkins said. "It's just a matter of when we see the water spilling over the levees."